src/librustc/traits/util.rs

   1 use crate::hir;
   2 use crate::hir::def_id::DefId;
   3 use crate::traits::specialize::specialization_graph::NodeItem;
   4 use crate::ty::{self, Ty, TyCtxt, ToPredicate, ToPolyTraitRef};
   5 use crate::ty::outlives::Component;
   6 use crate::ty::subst::{Kind, Subst, SubstsRef};
   7 use crate::util::nodemap::FxHashSet;
   8
   9 use super::{Obligation, ObligationCause, PredicateObligation, SelectionContext, Normalized};
  10
  11 fn anonymize_predicate<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
  12                                        pred: &ty::Predicate<'tcx>)
  13                                        -> ty::Predicate<'tcx> {
  14     match *pred {
  15         ty::Predicate::Trait(ref data) =>
  16             ty::Predicate::Trait(tcx.anonymize_late_bound_regions(data)),
  17
  18         ty::Predicate::RegionOutlives(ref data) =>
  19             ty::Predicate::RegionOutlives(tcx.anonymize_late_bound_regions(data)),
  20
  21         ty::Predicate::TypeOutlives(ref data) =>
  22             ty::Predicate::TypeOutlives(tcx.anonymize_late_bound_regions(data)),
  23
  24         ty::Predicate::Projection(ref data) =>
  25             ty::Predicate::Projection(tcx.anonymize_late_bound_regions(data)),
  26
  27         ty::Predicate::WellFormed(data) =>
  28             ty::Predicate::WellFormed(data),
  29
  30         ty::Predicate::ObjectSafe(data) =>
  31             ty::Predicate::ObjectSafe(data),
  32
  33         ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) =>
  34             ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind),
  35
  36         ty::Predicate::Subtype(ref data) =>
  37             ty::Predicate::Subtype(tcx.anonymize_late_bound_regions(data)),
  38
  39         ty::Predicate::ConstEvaluatable(def_id, substs) =>
  40             ty::Predicate::ConstEvaluatable(def_id, substs),
  41     }
  42 }
  43
  44
  45 struct PredicateSet<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  46     tcx: TyCtxt<'a, 'gcx, 'tcx>,
  47     set: FxHashSet<ty::Predicate<'tcx>>,
  48 }
  49
  50 impl<'a, 'gcx, 'tcx> PredicateSet<'a, 'gcx, 'tcx> {
  51     fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> PredicateSet<'a, 'gcx, 'tcx> {
  52         PredicateSet { tcx: tcx, set: Default::default() }
  53     }
  54
  55     fn insert(&mut self, pred: &ty::Predicate<'tcx>) -> bool {
  56         // We have to be careful here because we want
  57         //
  58         //    for<'a> Foo<&'a int>
  59         //
  60         // and
  61         //
  62         //    for<'b> Foo<&'b int>
  63         //
  64         // to be considered equivalent. So normalize all late-bound
  65         // regions before we throw things into the underlying set.
  66         self.set.insert(anonymize_predicate(self.tcx, pred))
  67     }
  68 }
  69
  70 ///////////////////////////////////////////////////////////////////////////
  71 // `Elaboration` iterator
  72 ///////////////////////////////////////////////////////////////////////////
  73
  74 /// "Elaboration" is the process of identifying all the predicates that
  75 /// are implied by a source predicate. Currently this basically means
  76 /// walking the "supertraits" and other similar assumptions. For
  77 /// example, if we know that `T : Ord`, the elaborator would deduce
  78 /// that `T : PartialOrd` holds as well. Similarly, if we have `trait
  79 /// Foo : 'static`, and we know that `T : Foo`, then we know that `T :
  80 /// 'static`.
  81 pub struct Elaborator<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  82     stack: Vec<ty::Predicate<'tcx>>,
  83     visited: PredicateSet<'a, 'gcx, 'tcx>,
  84 }
  85
  86 pub fn elaborate_trait_ref<'cx, 'gcx, 'tcx>(
  87     tcx: TyCtxt<'cx, 'gcx, 'tcx>,
  88     trait_ref: ty::PolyTraitRef<'tcx>)
  89     -> Elaborator<'cx, 'gcx, 'tcx>
  90 {
  91     elaborate_predicates(tcx, vec![trait_ref.to_predicate()])
  92 }
  93
  94 pub fn elaborate_trait_refs<'cx, 'gcx, 'tcx>(
  95     tcx: TyCtxt<'cx, 'gcx, 'tcx>,
  96     trait_refs: impl Iterator<Item = ty::PolyTraitRef<'tcx>>)
  97     -> Elaborator<'cx, 'gcx, 'tcx>
  98 {
  99     let predicates = trait_refs.map(|trait_ref| trait_ref.to_predicate())
 100                                .collect();
 101     elaborate_predicates(tcx, predicates)
 102 }
 103
 104 pub fn elaborate_predicates<'cx, 'gcx, 'tcx>(
 105     tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 106     mut predicates: Vec<ty::Predicate<'tcx>>)
 107     -> Elaborator<'cx, 'gcx, 'tcx>
 108 {
 109     let mut visited = PredicateSet::new(tcx);
 110     predicates.retain(|pred| visited.insert(pred));
 111     Elaborator { stack: predicates, visited: visited }
 112 }
 113
 114 impl<'cx, 'gcx, 'tcx> Elaborator<'cx, 'gcx, 'tcx> {
 115     pub fn filter_to_traits(self) -> FilterToTraits<Self> {
 116         FilterToTraits::new(self)
 117     }
 118
 119     fn push(&mut self, predicate: &ty::Predicate<'tcx>) {
 120         let tcx = self.visited.tcx;
 121         match *predicate {
 122             ty::Predicate::Trait(ref data) => {
 123                 // Predicates declared on the trait.
 124                 let predicates = tcx.super_predicates_of(data.def_id());
 125
 126                 let mut predicates: Vec<_> =
 127                     predicates.predicates
 128                               .iter()
 129                               .map(|(p, _)| p.subst_supertrait(tcx, &data.to_poly_trait_ref()))
 130                               .collect();
 131
 132                 debug!("super_predicates: data={:?} predicates={:?}",
 133                        data, predicates);
 134
 135                 // Only keep those bounds that we haven't already
 136                 // seen.  This is necessary to prevent infinite
 137                 // recursion in some cases.  One common case is when
 138                 // people define `trait Sized: Sized { }` rather than `trait
 139                 // Sized { }`.
 140                 predicates.retain(|r| self.visited.insert(r));
 141
 142                 self.stack.extend(predicates);
 143             }
 144             ty::Predicate::WellFormed(..) => {
 145                 // Currently, we do not elaborate WF predicates,
 146                 // although we easily could.
 147             }
 148             ty::Predicate::ObjectSafe(..) => {
 149                 // Currently, we do not elaborate object-safe
 150                 // predicates.
 151             }
 152             ty::Predicate::Subtype(..) => {
 153                 // Currently, we do not "elaborate" predicates like `X
 154                 // <: Y`, though conceivably we might.
 155             }
 156             ty::Predicate::Projection(..) => {
 157                 // Nothing to elaborate in a projection predicate.
 158             }
 159             ty::Predicate::ClosureKind(..) => {
 160                 // Nothing to elaborate when waiting for a closure's kind to be inferred.
 161             }
 162             ty::Predicate::ConstEvaluatable(..) => {
 163                 // Currently, we do not elaborate const-evaluatable
 164                 // predicates.
 165             }
 166
 167             ty::Predicate::RegionOutlives(..) => {
 168                 // Nothing to elaborate from `'a: 'b`.
 169             }
 170
 171             ty::Predicate::TypeOutlives(ref data) => {
 172                 // We know that `T: 'a` for some type `T`. We can
 173                 // often elaborate this. For example, if we know that
 174                 // `[U]: 'a`, that implies that `U: 'a`. Similarly, if
 175                 // we know `&'a U: 'b`, then we know that `'a: 'b` and
 176                 // `U: 'b`.
 177                 //
 178                 // We can basically ignore bound regions here. So for
 179                 // example `for<'c> Foo<'a,'c>: 'b` can be elaborated to
 180                 // `'a: 'b`.
 181
 182                 // Ignore `for<'a> T: 'a` -- we might in the future
 183                 // consider this as evidence that `T: 'static`, but
 184                 // I'm a bit wary of such constructions and so for now
 185                 // I want to be conservative. --nmatsakis
 186                 let ty_max = data.skip_binder().0;
 187                 let r_min = data.skip_binder().1;
 188                 if r_min.is_late_bound() {
 189                     return;
 190                 }
 191
 192                 let visited = &mut self.visited;
 193                 let mut components = smallvec![];
 194                 tcx.push_outlives_components(ty_max, &mut components);
 195                 self.stack.extend(
 196                     components
 197                        .into_iter()
 198                        .filter_map(|component| match component {
 199                            Component::Region(r) => if r.is_late_bound() {
 200                                None
 201                            } else {
 202                                Some(ty::Predicate::RegionOutlives(
 203                                    ty::Binder::dummy(ty::OutlivesPredicate(r, r_min))))
 204                            },
 205
 206                            Component::Param(p) => {
 207                                let ty = tcx.mk_ty_param(p.idx, p.name);
 208                                Some(ty::Predicate::TypeOutlives(
 209                                    ty::Binder::dummy(ty::OutlivesPredicate(ty, r_min))))
 210                            },
 211
 212                            Component::UnresolvedInferenceVariable(_) => {
 213                                None
 214                            },
 215
 216                            Component::Projection(_) |
 217                            Component::EscapingProjection(_) => {
 218                                // We can probably do more here. This
 219                                // corresponds to a case like `<T as
 220                                // Foo<'a>>::U: 'b`.
 221                                None
 222                            },
 223                        })
 224                        .filter(|p| visited.insert(p)));
 225             }
 226         }
 227     }
 228 }
 229
 230 impl<'cx, 'gcx, 'tcx> Iterator for Elaborator<'cx, 'gcx, 'tcx> {
 231     type Item = ty::Predicate<'tcx>;
 232
 233     fn size_hint(&self) -> (usize, Option<usize>) {
 234         (self.stack.len(), None)
 235     }
 236
 237     fn next(&mut self) -> Option<ty::Predicate<'tcx>> {
 238         // Extract next item from top-most stack frame, if any.
 239         let next_predicate = match self.stack.pop() {
 240             Some(predicate) => predicate,
 241             None => {
 242                 // No more stack frames. Done.
 243                 return None;
 244             }
 245         };
 246         self.push(&next_predicate);
 247         return Some(next_predicate);
 248     }
 249 }
 250
 251 ///////////////////////////////////////////////////////////////////////////
 252 // Supertrait iterator
 253 ///////////////////////////////////////////////////////////////////////////
 254
 255 pub type Supertraits<'cx, 'gcx, 'tcx> = FilterToTraits<Elaborator<'cx, 'gcx, 'tcx>>;
 256
 257 pub fn supertraits<'cx, 'gcx, 'tcx>(tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 258                                     trait_ref: ty::PolyTraitRef<'tcx>)
 259                                     -> Supertraits<'cx, 'gcx, 'tcx>
 260 {
 261     elaborate_trait_ref(tcx, trait_ref).filter_to_traits()
 262 }
 263
 264 pub fn transitive_bounds<'cx, 'gcx, 'tcx>(tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 265                                           bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>)
 266                                           -> Supertraits<'cx, 'gcx, 'tcx>
 267 {
 268     elaborate_trait_refs(tcx, bounds).filter_to_traits()
 269 }
 270
 271 ///////////////////////////////////////////////////////////////////////////
 272 // Iterator over def-ids of supertraits
 273
 274 pub struct SupertraitDefIds<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 275     tcx: TyCtxt<'a, 'gcx, 'tcx>,
 276     stack: Vec<DefId>,
 277     visited: FxHashSet<DefId>,
 278 }
 279
 280 pub fn supertrait_def_ids<'cx, 'gcx, 'tcx>(tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 281                                            trait_def_id: DefId)
 282                                            -> SupertraitDefIds<'cx, 'gcx, 'tcx>
 283 {
 284     SupertraitDefIds {
 285         tcx,
 286         stack: vec![trait_def_id],
 287         visited: Some(trait_def_id).into_iter().collect(),
 288     }
 289 }
 290
 291 impl<'cx, 'gcx, 'tcx> Iterator for SupertraitDefIds<'cx, 'gcx, 'tcx> {
 292     type Item = DefId;
 293
 294     fn next(&mut self) -> Option<DefId> {
 295         let def_id = self.stack.pop()?;
 296         let predicates = self.tcx.super_predicates_of(def_id);
 297         let visited = &mut self.visited;
 298         self.stack.extend(
 299             predicates.predicates
 300                       .iter()
 301                       .filter_map(|(p, _)| p.to_opt_poly_trait_ref())
 302                       .map(|t| t.def_id())
 303                       .filter(|&super_def_id| visited.insert(super_def_id)));
 304         Some(def_id)
 305     }
 306 }
 307
 308 ///////////////////////////////////////////////////////////////////////////
 309 // Other
 310 ///////////////////////////////////////////////////////////////////////////
 311
 312 /// A filter around an iterator of predicates that makes it yield up
 313 /// just trait references.
 314 pub struct FilterToTraits<I> {
 315     base_iterator: I
 316 }
 317
 318 impl<I> FilterToTraits<I> {
 319     fn new(base: I) -> FilterToTraits<I> {
 320         FilterToTraits { base_iterator: base }
 321     }
 322 }
 323
 324 impl<'tcx, I: Iterator<Item = ty::Predicate<'tcx>>> Iterator for FilterToTraits<I> {
 325     type Item = ty::PolyTraitRef<'tcx>;
 326
 327     fn next(&mut self) -> Option<ty::PolyTraitRef<'tcx>> {
 328         loop {
 329             match self.base_iterator.next() {
 330                 None => {
 331                     return None;
 332                 }
 333                 Some(ty::Predicate::Trait(data)) => {
 334                     return Some(data.to_poly_trait_ref());
 335                 }
 336                 Some(_) => {}
 337             }
 338         }
 339     }
 340
 341     fn size_hint(&self) -> (usize, Option<usize>) {
 342         let (_, upper) = self.base_iterator.size_hint();
 343         (0, upper)
 344     }
 345 }
 346
 347 ///////////////////////////////////////////////////////////////////////////
 348 // Other
 349 ///////////////////////////////////////////////////////////////////////////
 350
 351 /// Instantiate all bound parameters of the impl with the given substs,
 352 /// returning the resulting trait ref and all obligations that arise.
 353 /// The obligations are closed under normalization.
 354 pub fn impl_trait_ref_and_oblig<'a, 'gcx, 'tcx>(selcx: &mut SelectionContext<'a, 'gcx, 'tcx>,
 355                                                 param_env: ty::ParamEnv<'tcx>,
 356                                                 impl_def_id: DefId,
 357                                                 impl_substs: SubstsRef<'tcx>,)
 358                                                 -> (ty::TraitRef<'tcx>,
 359                                                     Vec<PredicateObligation<'tcx>>)
 360 {
 361     let impl_trait_ref =
 362         selcx.tcx().impl_trait_ref(impl_def_id).unwrap();
 363     let impl_trait_ref =
 364         impl_trait_ref.subst(selcx.tcx(), impl_substs);
 365     let Normalized { value: impl_trait_ref, obligations: normalization_obligations1 } =
 366         super::normalize(selcx, param_env, ObligationCause::dummy(), &impl_trait_ref);
 367
 368     let predicates = selcx.tcx().predicates_of(impl_def_id);
 369     let predicates = predicates.instantiate(selcx.tcx(), impl_substs);
 370     let Normalized { value: predicates, obligations: normalization_obligations2 } =
 371         super::normalize(selcx, param_env, ObligationCause::dummy(), &predicates);
 372     let impl_obligations =
 373         predicates_for_generics(ObligationCause::dummy(), 0, param_env, &predicates);
 374
 375     let impl_obligations: Vec<_> =
 376         impl_obligations.into_iter()
 377         .chain(normalization_obligations1)
 378         .chain(normalization_obligations2)
 379         .collect();
 380
 381     (impl_trait_ref, impl_obligations)
 382 }
 383
 384 /// See `super::obligations_for_generics`
 385 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
 386                                      recursion_depth: usize,
 387                                      param_env: ty::ParamEnv<'tcx>,
 388                                      generic_bounds: &ty::InstantiatedPredicates<'tcx>)
 389                                      -> Vec<PredicateObligation<'tcx>>
 390 {
 391     debug!("predicates_for_generics(generic_bounds={:?})",
 392            generic_bounds);
 393
 394     generic_bounds.predicates.iter().map(|predicate| {
 395         Obligation { cause: cause.clone(),
 396                      recursion_depth,
 397                      param_env,
 398                      predicate: predicate.clone() }
 399     }).collect()
 400 }
 401
 402 pub fn predicate_for_trait_ref<'tcx>(
 403     cause: ObligationCause<'tcx>,
 404     param_env: ty::ParamEnv<'tcx>,
 405     trait_ref: ty::TraitRef<'tcx>,
 406     recursion_depth: usize)
 407     -> PredicateObligation<'tcx>
 408 {
 409     Obligation {
 410         cause,
 411         param_env,
 412         recursion_depth,
 413         predicate: trait_ref.to_predicate(),
 414     }
 415 }
 416
 417 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 418     pub fn predicate_for_trait_def(self,
 419                                    param_env: ty::ParamEnv<'tcx>,
 420                                    cause: ObligationCause<'tcx>,
 421                                    trait_def_id: DefId,
 422                                    recursion_depth: usize,
 423                                    self_ty: Ty<'tcx>,
 424                                    params: &[Kind<'tcx>])
 425         -> PredicateObligation<'tcx>
 426     {
 427         let trait_ref = ty::TraitRef {
 428             def_id: trait_def_id,
 429             substs: self.mk_substs_trait(self_ty, params)
 430         };
 431         predicate_for_trait_ref(cause, param_env, trait_ref, recursion_depth)
 432     }
 433
 434     /// Cast a trait reference into a reference to one of its super
 435     /// traits; returns `None` if `target_trait_def_id` is not a
 436     /// supertrait.
 437     pub fn upcast_choices(self,
 438                           source_trait_ref: ty::PolyTraitRef<'tcx>,
 439                           target_trait_def_id: DefId)
 440                           -> Vec<ty::PolyTraitRef<'tcx>>
 441     {
 442         if source_trait_ref.def_id() == target_trait_def_id {
 443             return vec![source_trait_ref]; // shorcut the most common case
 444         }
 445
 446         supertraits(self, source_trait_ref)
 447             .filter(|r| r.def_id() == target_trait_def_id)
 448             .collect()
 449     }
 450
 451     /// Given a trait `trait_ref`, returns the number of vtable entries
 452     /// that come from `trait_ref`, excluding its supertraits. Used in
 453     /// computing the vtable base for an upcast trait of a trait object.
 454     pub fn count_own_vtable_entries(self, trait_ref: ty::PolyTraitRef<'tcx>) -> usize {
 455         let mut entries = 0;
 456         // Count number of methods and add them to the total offset.
 457         // Skip over associated types and constants.
 458         for trait_item in self.associated_items(trait_ref.def_id()) {
 459             if trait_item.kind == ty::AssociatedKind::Method {
 460                 entries += 1;
 461             }
 462         }
 463         entries
 464     }
 465
 466     /// Given an upcast trait object described by `object`, returns the
 467     /// index of the method `method_def_id` (which should be part of
 468     /// `object.upcast_trait_ref`) within the vtable for `object`.
 469     pub fn get_vtable_index_of_object_method<N>(self,
 470                                                 object: &super::VtableObjectData<'tcx, N>,
 471                                                 method_def_id: DefId) -> usize {
 472         // Count number of methods preceding the one we are selecting and
 473         // add them to the total offset.
 474         // Skip over associated types and constants.
 475         let mut entries = object.vtable_base;
 476         for trait_item in self.associated_items(object.upcast_trait_ref.def_id()) {
 477             if trait_item.def_id == method_def_id {
 478                 // The item with the ID we were given really ought to be a method.
 479                 assert_eq!(trait_item.kind, ty::AssociatedKind::Method);
 480                 return entries;
 481             }
 482             if trait_item.kind == ty::AssociatedKind::Method {
 483                 entries += 1;
 484             }
 485         }
 486
 487         bug!("get_vtable_index_of_object_method: {:?} was not found",
 488              method_def_id);
 489     }
 490
 491     pub fn closure_trait_ref_and_return_type(self,
 492         fn_trait_def_id: DefId,
 493         self_ty: Ty<'tcx>,
 494         sig: ty::PolyFnSig<'tcx>,
 495         tuple_arguments: TupleArgumentsFlag)
 496         -> ty::Binder<(ty::TraitRef<'tcx>, Ty<'tcx>)>
 497     {
 498         let arguments_tuple = match tuple_arguments {
 499             TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
 500             TupleArgumentsFlag::Yes =>
 501                 self.intern_tup(sig.skip_binder().inputs()),
 502         };
 503         let trait_ref = ty::TraitRef {
 504             def_id: fn_trait_def_id,
 505             substs: self.mk_substs_trait(self_ty, &[arguments_tuple.into()]),
 506         };
 507         ty::Binder::bind((trait_ref, sig.skip_binder().output()))
 508     }
 509
 510     pub fn generator_trait_ref_and_outputs(self,
 511         fn_trait_def_id: DefId,
 512         self_ty: Ty<'tcx>,
 513         sig: ty::PolyGenSig<'tcx>)
 514         -> ty::Binder<(ty::TraitRef<'tcx>, Ty<'tcx>, Ty<'tcx>)>
 515     {
 516         let trait_ref = ty::TraitRef {
 517             def_id: fn_trait_def_id,
 518             substs: self.mk_substs_trait(self_ty, &[]),
 519         };
 520         ty::Binder::bind((trait_ref, sig.skip_binder().yield_ty, sig.skip_binder().return_ty))
 521     }
 522
 523     pub fn impl_is_default(self, node_item_def_id: DefId) -> bool {
 524         match self.hir().as_local_hir_id(node_item_def_id) {
 525             Some(hir_id) => {
 526                 let item = self.hir().expect_item_by_hir_id(hir_id);
 527                 if let hir::ItemKind::Impl(_, _, defaultness, ..) = item.node {
 528                     defaultness.is_default()
 529                 } else {
 530                     false
 531                 }
 532             }
 533             None => {
 534                 self.global_tcx()
 535                     .impl_defaultness(node_item_def_id)
 536                     .is_default()
 537             }
 538         }
 539     }
 540
 541     pub fn impl_item_is_final(self, node_item: &NodeItem<hir::Defaultness>) -> bool {
 542         node_item.item.is_final() && !self.impl_is_default(node_item.node.def_id())
 543     }
 544 }
 545
 546 pub enum TupleArgumentsFlag { Yes, No }